1. Field of the Invention
The present invention relates to a method for manufacturing a transmitter module, a receiver module, etc. employed to compose a light transmission system at a high yield, and inspecting each of those modules for a character of its low bit error rate (BER: a bit error rate of a signal output from a receiver to the number of random patterns of a signal entered to a transmitter or a disagreement rate of a signal pattern output from the receiver to a signal pattern entered to the transmitter) quickly and accurately with respect to a propagated optical power, as well as a system and a method for inspecting those manufactured modules easily, quickly, and accurately. More particularly, the present invention relates to inspection of optic transmission modules employed for composing a light transmission system for such characters as minimum received power sensitivity, dependency of an optical power by rate, propagation penalty, etc., that is, techniques for measuring, inspecting, and testing fast light/electrical signals.
2. Description of Related Art
To measure a character of a bit error rate (BER), which is the first related art technique, an error rate measuring instrument is used in accordance to the object propagation velocity. In this case, the number of errors is counted and the error rate is calculated within a predetermined time of a received signal light both when the transmitter and the receiver are directly connected to each other and when they are connected to each other via a long distance fiber line. It is premised here that both transmitter and receiver are not disturbed by any interference light. Usually, it takes about ten minutes per BER curve to measure a BER character of about 10xe2x88x923 to 10xe2x88x9212. In addition, because such a BER curve must be measured according to the fluctuation of the ambient temperature and the fluctuation of the power supply of the transmission/receiver module, it takes about a few hours to inspect each object module.
Furthermore, because it takes a few hours to several tens of hours to measure a BER character whose order is as low as 10xe2x88x9213 and 10xe2x88x9214, it is confirmed that no error occurs in bit error measurements at an optical power, which is a few dBm higher than an optical power when the BER character of 10xe2x88x9210 is obtained with addition of an interference light employed as one-point data.
The second related art technique is a sinusoidal wave interference method, which is disclosed in the document (Margin Measurements in Optical Amplifier Systems: IE3 PHOTONICS TECHNOLOGY LETTER, VOL.5, NO.3, MARCH 1993). According to this method, both amplitude and BER of a sinusoidal wave signal are used for extrapolating the BER, so that the extrapolation comes to be possible for up to about 10xe2x88x9220.
The third related art technique is a method for measuring a bit error rate with addition of a noise, thereby calculating and estimating a bit error rate when no degradation is recognized, as disclosed in Japanese Published Unexamined Patent Application No.6-252959. In this method, a relative phase of a demodulated output is identified both before and after a noise is added, thereby calculating the BER.
In recent years, however, it has been demanded to measure a lower bit error rate of 10xe2x88x9212 or under, since information communication systems are getting faster and faster in operation and larger and larger in capacity so as to meet the requirement of a higher reliability of fast optical communication systems.
The first related art technique, however, has been confronted with problems that it takes a long time to a non-actual extent, as well as a predetermined accuracy cannot be guaranteed for the result.
The second related art technique has also been confronted with problems that a predetermined accuracy cannot be guaranteed in inspection, since a sinusoidal wave signal must be changed in amplitude and modified, thus difficult to be controlled. In addition, it would take more than a thousand year to confirm an extrapolation accuracy and a relative error in the conventional measurement in real time on the level of 10xe2x88x9220.
The third related art technique has also been confronted with a problem that a predetermined accuracy cannot be guaranteed in inspection, since the identification process is too complicated.
Under the circumstances, it is an object of the present invention to provide a method for manufacturing optic transmission modules, which can assure a high reliability for each of those optic transmission modules in quick and accurate inspection of the character of its low bit error rate (BER) so as to be employed satisfactorily for an optical communication system (a light transmission system) required to cope with information communication systems that are getting faster and faster in operation and larger and larger in capacity, thereby solving the above related art problems, as well as a system and a method for inspecting the character of such a bit error rate (BER).
It is another object of the present invention to provide a method for manufacturing high quality optic transmission modules at a high yield by quick and accurate inspection each of those optic transmission modules with respect to the character of its low bit error rate (BER) so as to be employed satisfactorily for an optical communication system (light transmission system) required to cope with information communication systems that are getting faster and faster in operation and larger and larger in capacity.
In order to achieve the above objects, the method of the present invention for manufacturing optic transmission modules comprises the processes of;
(A) manufacturing an optic transmission module employed for a light transmission system; and
(B) inspecting the optic transmission module manufactured in the manufacturing process for a character of its bit error rate with use of a bit error rate specific inspection system; wherein
the bit error rate specific inspection system includes;
signal light transmitting means for generating a light signal according to an electrical signal pattern;
interference light transmitting means for generating an interference light according to a disturbance signal having a rectangular pulse waveform;
a light coupler for mixing the signal light received from the signal light transmitting means optionally with the interference light received from the interference light transmitting means;
optical means for changing the optical power of the mixed light received from the light coupler;
receiving means for converting the mixed light received from the optical means to an electrical signal so as to be identified and regenerated; and
calculating means for measuring a bit error rate of the mixed signal regenerated by the receiving means corresponding to the optical power of the mixed light changed by the optical means, thereby calculating a character of a bit error rate of a signal light to its optical power according to this measured bit error rate corresponded to the change of the optical power of the mixed light, then generating a character of a bit error rate when no interference light is detected on the basis of a theoretical character of a bit error rate according to this calculated character of the bit error rate of the signal light to its optical power so as to be inspected.
Furthermore, in order to achieve the above objects, the method of the present invention for:manufacturing optic transmission modules comprises the processes of;
(A) manufacturing an optic transmission module employed for a light transmission system; and
(B) inspecting a character of a bit error rate of the optic transmission module manufactured in the manufacturing process with use of a bit error rate specific inspection system; wherein
the bit error rate specific inspection system includes;
signal light transmitting means for generating a light signal according to an electrical signal pattern;
interference light transmitting means for generating an interference light according to a disturbance signal having a rectangular pulse waveform;
a light coupler for mixing the signal light received from the signal light transmitting means optically with the interference light received from the interference light transmitting means;
optical means for setting an (S/X) ratio of an optical power of the signal light to an optical power of the interference light mixed by the light coupler to a predetermined value so as to change the optical power of the mixed light;
receiving means for converting the mixed light received from the optical means to an electrical signal so as to be identified and regenerated; and
calculating means for measuring a bit error rate of the mixed signal regenerated by the receiving means corresponding to a change of the optical power of the mixed light at the optical power ratio (S/X) set by the optical means, thereby calculating a character of a bit error rate of a signal light to its optical power at the optical power ratio (S/X) according to this measured bit error rate corresponded to the change of the optical power of the mixed light at this measured optical power ratio (S/X), then generating a character of a bit error rate when no interference light is detected on the basis of a theoretical character of a bit error rate according to this calculated character of the bit error rate of the signal light to its optical power at the optical power ratio (S/X) so as to be inspected.
Furthermore, the method of the present invention for manufacturing optic transmission modules employed for a light transmission system and provided with a transmitter and a receiver respectively comprises the processes of;
(A) manufacturing an optic transmission module provided with a transmitter and a receiver and employed for the light transmission system; and
(B) inspecting the optic transmission module manufactured in the manufacturing process for its bit error rate; wherein
the inspection process makes it possible that the transmitter receives a pattern signal and outputs a signal light, which is mixed with a pulse-like interference light into a light signal, then the receiver receives the mixed slight signal and outputs a signal, which is measured, thereby a bit error rate of a pattern of the output signal received from the receiver is found so that a bit error rate of a pattern of the output signal to the pattern input signal is calculated according to the measured bit error rate when no interference light is detected.
Furthermore, the method of the present invention for manufacturing optic transmission modules comprises the processes of;
(A) manufacturing an optic transmission module employed for a light transmission system; and
(B) inspecting the optic transmission module for its bit error rate; wherein
the inspection process makes it possible that;
a pattern signal is entered to the transmitter of the optic transmission module;
a signal light output from the transmitter according to an input of the pattern signal is mixed with a pulse-like interference light having a frequency smaller than a signal frequency of the signal light;
the mixed light is entered to the receiver of the optic transmission module via an optical fiber line;
an output signal from the receiver that has received the mixed light is measured, thereby finding a bit error rate of a pattern of the output signal received from the receiver to a pattern signal entered to the receiver, then calculating a bit error rate of an output signal from the receiver to a pattern signal entered to the transmitter when no interference light is detected from the optic transmission module.
Furthermore, the bit error rate specific inspection system of the present invention, which is employed for a light transmission system and composed so as to inspect an object inspection module for a character of its bit error rate, comprising:
signal light transmitting means for generating a light signal according to an electrical signal pattern;
interference light transmitting means for generating an interference light according to a disturbance signal having a rectangular pulse waveform;
a light coupler for mixing the signal light received from the signal light transmitting means optically with the interference light received from the interference light transmitting means;
optical means for changing the optical power of the mixed light received from the light coupler;
receiving means for converting the mixed light received from the optical means to an electrical signal so as to be identified and regenerated; and
calculating means for measuring a bit error rate of the mixed signal regenerated by the receiving means corresponding to the optical power of the mixed light changed by the optical means, thereby calculating a character of a bit error rate of a signal light to its optical power according to this measured bit error rate corresponded to the change of the optical power of the mixed light, then generating a character of a bit error rate when no interference light is detected on the basis of a theoretical character of a bit error rate according to this calculated character of the bit error rate of the signal light to its optical power so as to be inspected.
Furthermore, the bit error rate specific inspection system of the present invention, which is employed for a light transmission system and composed so as to inspect an inspection object for a character of its bit error rate, comprising:
signal light transmitting means for generating a light signal according to an electrical signal pattern;
interference light transmitting means for generating an interference light according to a disturbance signal having a rectangular pulse waveform;
a light coupler for mixing the signal light received from the signal light transmitting means with the interference light received from the interference light transmitting means;
optical means for setting an (S/X) ratio of an optical power of the signal light to an optical power of the interference light mixed by the light coupler to a predetermined value so as to change the optical power of the mixed light;
receiving means for converting the mixed light received from the optical means to an electrical signal so as to be identified and regenerated; and
calculating means for measuring a bit error rate of the mixed signal regenerated by the receiving means corresponding to a change of the optical power of the mixed light at the optical power ratio (S/X) set by the optical means, thereby calculating a character of a bit error rate of a signal light to its optical power at the optical power ratio (S/X) according to this measured bit error rate corresponded to the change of the optical power of the mixed light at the optical power ratio (S/X), then generating a character of a bit error rate when no interference light is detected on the basis of a theoretical character of a bit error rate according to this calculated character of the bit error rate of the signal light to its optical power at the optical power ratio (S/X) so as to be inspected.
The bit error rate specific inspection system of the present invention for inspecting an optic transmission module employed for a light transmission system for a bit error rate, comprising:
pattern signal generating means for generating a pattern signal to be entered to a transmitter of the optic transmission module;
transmitting means for receiving the pattern signal generated in the pattern signal generating means, thereby generating a first light signal;
pulse-like signal generating means for generating a pulse-like signal;
signal converting means for generating a second light signal from a pulse-like signal generated in the pulse-like signal generating means;
light mixing means for mixing the first light signal with the second light signal, thereby outputting a mixed light;
receiving means for receiving a mixed light output from the light mixing means; and
calculating means for receiving a pattern signal generated in the pattern signal generating means and a pattern signal output from the receiving means, thereby finding a bit error rate of a pattern of an output signal from the receiver to a pattern signal entered to a transmitter of the transmitting means, the receiving means, or the optical fiber means, thereby calculating a bit error rate of a pattern of an output signal from the receiver to a pattern signal entered to the transmitter according to the found error bit rate when no interference light is detected from the transmitting means, the receiving means, or the optical fiber means.
Furthermore, the method of the present invention for inspecting an object optic module employed for a light transmission system for a bit error rate comprises the processes of;
(A) generating a light signal from a transmitter;
(B) generating an interference light, which is a digital light signal of a lower frequency than that of the light signal;
(C) mixing the light signal with the interference signal;
(D) attenuating the power of the mixed light signal;
(E) receiving the attenuated light signal at a receiver and measuring a bit error rate of the received signal;
(F) calculating the bit error rate, thereby finding a character of a bit error rate when no interference light is detected (X=0);
(G) comparing the character of this found bit error rate with the character of a reference bit error rate, thereby deciding whether the character is OK or NG; and
(H) inspecting the bit error rate of an object optic module.
According to the methods of the present invention as described above, because a rectangular wave pulse is used as an interference light, it is possible to calculate degradation quantity of a simple theoretical signal-noise ratio (SIN). Consequently, a case in which there is no interference light (S/X=∞ or X=0) can be extrapolated from a bit error rate of a measured light signal with use of a theoretical value of a sign bit error rate. In addition, an accurate character can be generated for a low bit error rate (BER) of 10xe2x88x9212 or under easily according to an optical power ratio between optical powers of a signal light and an interference light (S/X value), thereby enabling inspection of a low bit error rate of 10xe2x88x9212 or under to be made accurately, easily, and quickly. As a result, the present invention can assure a high reliability for optical communication systems (light transmission systems) required so as to cope with faster and larger capacity information communication systems (which has a capacity of more than 2.4 Gbits/,for example, 10 Gbits/sec and 40 G bits/sec, etc.).